A mobile station, also known as a User Equipment (UE), wireless terminal and/or mobile terminal is enabled to communicate wirelessly in a wireless communication network, some-times also referred to as a cellular radio system. The communication may be made, e.g., between user equipment, between a user equipment and a wire connected telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks. The wireless communication may comprise various communication services such as voice, messaging, packet data, video, broadcast, etc.
The mobile station may further be referred to as mobile telephone, cellular telephone, computer tablet or laptop with wireless capability, etc. The mobile station in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another mobile station, a stationary entity or a server.
The wireless communication network covers a geographical area which is divided into cell areas, with each cell area being served by a network node, radio network node or base station, e.g., a Radio Base Station (RBS) or Base Transceiver Station (BTS), which in some networks may be referred to as “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and/or terminology used.
Sometimes, the expression “cell” may be used for denoting the network node itself. However, the cell may also in normal terminology be used for the geographical area where radio coverage is provided by the network node at a base station site. One network node, situated on the base station site, may serve one or several cells. The network nodes may communicate over the air interface operating on radio frequencies with any mobile station within range of the respective network node.
In some radio access networks, several network nodes may be connected, e.g., by land-lines or microwave, to a Radio Network Controller (RNC), e.g., in Universal Mobile Telecommunications System (UMTS). The RNC, also sometimes termed Base Station Controller (BSC), e.g., in GSM, may supervise and coordinate various activities of the plural radio network nodes connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), network nodes, which may be referred to as eNodeBs or eNBs, may be connected to a gateway, e.g., a radio access gateway, to one or more core networks. LTE is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements.
LTE-Advanced, i.e. LTE Release10 and later releases are set to provide higher bitrates in a cost efficient way and, at the same time, completely fulfil the requirements set by International Telecommunication Union (ITU) for the International Mobile Telecommunications (IMT)-Advanced, also referred to as 4G.
In the present context, the expressions downlink, downstream link or forward link may be used for the transmission path from the network node to the mobile station. The expression uplink, upstream link or reverse link may be used for the transmission path in the opposite direction, i.e., from the mobile station to the network node.
Densification of radio network nodes is expected to lead to the spectral efficiency requirements envisioned for future radio access networks. However studies have showed that a plain network densification would significantly increase the overall energy costs. Therefore, future generations of dense radio access network should be co-designed to be both spectral- and energy-efficient. Energy-efficient solutions are an advantage at the network side, e.g., to reduce running costs, and at the mobile station devices to increase battery lifetime and improve the user experience.
One method to achieve energy saving at the network side, is to enable radio access network nodes to operate in a discontinuous transmission (DTX) mode with a short active period of time, e.g. when there is traffic to be served, followed by a long dormant state (a.k.a. “off-state”) with limited transmission and reception capabilities. Future releases of the related art 3GPP Long Term Evolution (LTE) system shall adopt this feature for enhanced small cell operation (i.e., network nodes with a small coverage area), e.g., by dynamically switching on/off network nodes to follow traffic variations or other relevant network statistics.
However, solutions that enable energy saving at the network side may in fact determine higher energy consumption for some of the basic operations of the mobile station. For example, with network nodes enabled to operate in a DTX mode some or all the signals typically transmitted to aid the mobile station detect a network node, synchronize to, and measure the signal strength may either be absent or transmitted only sporadically. Therefore, procedures such as cell search, handover, Radio Resource Management (RRM) measurements, Radio Link Management (RLM) measurements, etc., designed for a system where network nodes are always active can become inefficient when network nodes operate in a DTX mode, thereby incurring in higher energy consumption at the mobile station device.
For instance, the 3GPP LTE-Advanced Rel.12 system shall introduce downlink Discovery Reference Signals (DRS) transmitted by network nodes in the dormant state of a DTX mode to aid and speed up the detection of dormant network nodes at the mobile station. However, the current LTE system design does not provide any means to directly control the energy saving at the mobile station when monitoring network nodes operating in DTX mode, or for other fundamental operations of the mobile station, such as cellsearch, handover, RRM measurements, RLM measurements, etc.
Therefore, methods for controlling and/or enabling energy saving at the mobile stations that account for the mobile station's energy status or other energy saving information associated with the mobile station can be beneficial in existing or future radio communication systems.
In a first prior art method for energy saving in a 3GPP LTE-A system, mobile stations may be configured with a Discontinuous Reception (DRX) mode and, in case of High Speed Packet Access (HSPA), a Discontinuous Transmission (DTX) mode for maximizing the battery lifetime. In DRX mode, the mobile station is configured to monitor downlink control signaling in only one subframe per DRX cycle, while sleeping with the receiver circuitry switched off in the remaining subframes.
A drawback of the first prior art method is that the configuration of the DRX mode for a mobile station does not depend on any feedback from the mobile station. It may be beneficial, for instance from a performance point of view, to not apply any DRX for a mobile station with fully loaded battery.
In a second prior art method, a mobile node is enabled to transmit at least one network energy saving information to a network control node associated to a preferred or accepted network energy saving mode, i.e., whether the mobile station accepts to participate in network energy saving and/or how much the mobile station would like to contribute to network energy saving. By collecting information from multiple mobile stations, the network control node can enable network energy saving through one or more transmission schemes, such as discontinuous transmission and/or reception, antenna transmission techniques, e.g., Multiple Input Multiple Output (MIMO) schemes, base station sector switching, multi-hop transmission, radio access technology switching, etc.
A drawback with the second prior art method is that it does not provide, or even aim at providing, any energy saving for the mobile station, but rather on the network side. The feedback from the mobile station is intended to determine a configuration of transmission scheme for network energy saving. The feedback information transmitted by the mobile station rather confirm that the mobile station is willing to participate in network energy saving.
In a third prior art method, network assistance associated to the configuration of Discovery Reference Signals (DRS) is provided by the serving network node to the served mobile station to aid monitoring network nodes operating in DTX mode. Network assistance may include information associated to one or more in the group of: a rough synchronization timing of one or multiple network nodes operating in DTX mode, so as to reduce the effort of the mobile station, for cell detection by avoiding synchronizing to the cells cluster; Physical cell ID (PCI) information to identify the neighboring network nodes in dormant state that the mobile station is required to monitor; type of DRS signal, e.g., time-frequency pattern, antenna port etc.
A drawback of the third prior art method is that the information provided by network assistance aims at improving only the detection probability of the other network nodes operating in DTX mode, not the energy efficiency of said operation. Thus, a mobile station with medium/low battery may be configured with parameters that improve the detection of dormant nodes by persistent monitoring of downlink signals transmitted by network nodes in DTX mode, thereby requiring even higher energy consumption at the mobile station.
In a fourth prior art, network assistance provides timing information associated to the reactivation time of other network nodes operating in DTX mode to be monitored, so as to enable the mobile station determine whether and when to monitor a dormant network node.
A drawback with the fourth prior art is that the network shall maintain a tight control over the mobile station with frequent information updates at the cost of large signaling overhead.
In a fifth prior art, a network node in dormant state encodes timing information associated with its reactivation time within a discovery reference signal, thereby enabling the mobile station to determine whether to continue monitoring the dormant node and perform initial synchronization and measurements (e.g., if the reactivation time is imminent) or resume monitoring the network node at a later time, thus saving energy.
A drawback of the fifth prior art is a potentially high detection complexity at the mobile station due to the number of cases to be tested by, for instance, blind decoding, thereby reducing the energy efficiency of the discovery of dormant network nodes.
Therefore, the cited prior art does not provide an efficient solution to directly control energy saving at the mobile station.